The journal, "Elektronik"2, Jan. 23, 1987 pp. 89-96, in particular pp. 92-93, describes a process in which an electrical signal is sampled with a sampling rate corresponding to an integer multiple of the fundamental component's frequency after analog pre-filtering. According to an example given, sampling is performed at a sampling rate of 2.56 kHz, and the spectral lines up to the sixth harmonic oscillation are determined in addition to the spectral line of a 160 Hz fundamental frequency. The spectral lines of the higher harmonics are greater than half the sampling rate (Nyquist frequency) and for real input signals provide the same values as the first eight spectral lines due to mirroring on the Nyquist frequency. The spectral lines of the higher harmonics can not, therefore, be selected and determined with such a process for a sampling frequency of 2.56 kHz. If these spectral lines are also to be determined with this conventional method, a sampling frequency twice as high, i.e., a sampling frequency of 5.12 kHz, would be required.